1. Field of the Invention
The present invention relates to an improved process for the preparation of polyalkenylsuccinic acid derivatives from oligo- and polyolefins and maleic acid derivatives and their use as fuel and lubricant additives. The present invention furthermore relates to fuels for gasoline engines and lubricants which contain these polyalkenylsuccinic acid derivatives, and ashless dispersants which are cocondensation products based on these polyalkenylsuccinic acid derivatives.
Polyisobutenylsuccinimides are widely used as ashless dispersants in the lubricant sector. They are present in an amount of up to 10% by weight in engine oils for gasoline and diesel engines and are intended here to prevent the agglomeration of particles, which is referred to in general as sludge formation. The dispersing effect, ie. in this case the imparting of water repellent properties to the particles, is therefore their most important property. In fuels, such compounds are used for keeping the intake system, in particular the intake valves, clean. In recent years, there has been an increasing tendency to replace the polyisobutene radical by other oligoolefin radicals. The requirements for these oligoolefin radicals are comparable with those for the polyisobutene radical.
The corresponding imides are generally prepared from polyamines and polyisobutenylsuccinic anhydride (PIBSA) by condensation. The preparation of PIBSA depends essentially on the polyisobutene (PIB) quality and is effected purely thermally (ene reaction), generally at from 225.degree. to 245.degree. C., with yields of about 65%. The yields can be increased to 90% by adding halogens. By an addition reaction with chlorine and dehydrohalogenation or allylchlorination, the double bond of the PIB can be activated and the reaction temperatures thus reduced to about 170.degree. C. However, the addition of chlorine leads in all cases to chlorine-containing compounds, and the combustion thereof in the engine generally leads to toxic dioxins in the exhaust gases.
2. Description of Related Art
According to U.S. Pat. No. 4,152,499 (1), with an increase in the vinylidene content in the PIB, ie. with higher content of reactive terminal double bonds, lower temperatures down to about 170.degree. C. can be realised in the ene reaction even without the use of halogen. According to the examples, however, the maleation of PIB is carried out at 200.degree. C. with a monomolar excess of maleic anhydride (MA) in order to obtain the yields required for marketing. Furthermore, such a type of reaction results in the formation of tar and opaque products which increase the acid and saponification number of the reaction products after removal of unconverted MA and thus simulate high yields.
U.S. Pat. No. 5,137,980 (2) discloses that polyisobutenes having a high vinylidene content give good results with low tar formation, preferably at from 220.degree. to 265.degree. C., with an excess of from 0.1 to 0.9 mol of MA and at from 4 to 50 bar. However, no information is given about the PIB conversion and the bismaleation fraction. In some cases, the reactions are carried out in the presence of catalysts, such as aluminum chloride, which are difficult to separate off.
DE-A 43 19 672 (3) discloses a process for the preparation of -polyisobutylsuccinic anhydrides from polyisobutene and maleic anhydride, in which polyisobutene containing at least 50% of terminal double bonds is reacted with excess maleic anhydride at from 140.degree. to 200.degree. C. The polyisobutylsuccinic anhydrides thus prepared can be further reacted with aliphatic polyamines to give the corresponding succinamides or succinimides. This preparation process for polyisobutylsuccinic anhydrides which usually gives a small bismaleation fraction does however also have disadvantages, in particular the unsatisfactory yields.
Since PIBSA having a low bismaleation fraction is desirable for certain industrial applications, it is an object of the present invention to provide a process for the preparation of polyalkenylsuccinic acid derivatives which gives products with little or no bismaleation fraction with simultaneously high conversions and good product quality.